1. Field of the Invention
The invention is generally related to an active device array substrate and a fabrication method thereof. More particularly, the invention is related to an active device array substrate capable of improving liquid crystal disclination and a fabrication method thereof.
2. Description of Related Art
With advantages of high definition, small volume, light weight, low driving voltage, low power consumption, and a wide range of applications, a liquid crystal display (LCD) panel has become the mainstream display product in the next generation. The conventional liquid crystal display panel is formed by a color filter substrate, a thin film transistor (TFT) array substrate and a liquid crystal layer sandwiched therebetween. In order to enhance the resolution and the aperture ratio of the LCD panel while also correcting the misalignment when the color filter substrate is joined to the TFT array substrate, a technique of directly integrating the color filter on the pixel array (i.e. Color Filter on Array, or COA) has been proposed.
FIG. 1A is a schematic top view illustrating a conventional active device array substrate. FIG. 1B is a schematic cross-sectional view illustrating a cross-section along a I-I′ line depicted in the conventional active device array substrate of FIG. 1A. Referring to FIGS. 1A and 1B, a conventional active device array substrate 100 includes a substrate 110, a plurality of scan lines 120 disposed on the substrate 110, a plurality of data lines 130 disposed on the substrate 110, a plurality of active devices 140 disposed on the substrate 110, a first passivation layer 150, a black matrix layer 160, a plurality of color filter patterns 170, a second passivation layer 180, and a plurality of pixel electrodes 190. By shielding the light emitted from the backlight module (not shown), the aforementioned black matrix layer 160 can shield the light input from the outer surface (i.e. the surface which does not have the active devices disposed thereon) of the substrate 110. Moreover, a material of the black matrix layer 160 is composed of opaque materials or opaque dye materials. In addition, a common line coupled to a common voltage of 0 V, for example, is depicted in FIG. 1A as the unlabeled lines located at the upper and lower sides of the scan lines 120 and arranged parallel to the scan lines 120. Each of the active devices 140 has a gate 140G, a source 140S, a drain 140D, and a channel layer 140C, in which the gate 140G is electrically connected to one of the scan lines 120, the source 140S is electrically connected to one of the data lines 130, and each drain 140D is electrically connected to one of the pixel electrodes 190 respectively. The first passivation layer 150 covers a gate insulating layer GI, the scan lines 120, the data lines 130, and the active devices 140. The black matrix layer 160 is disposed on the first passivation layer 150, wherein the black matrix layer 160 has a plurality of openings 160a, and the black matrix layer 160 is located above the scan lines 120 and the data lines 130.
The color filter patterns 170 are disposed in the openings 160a. The second passivation layer 180 is conformally disposed on the black matrix layer 160 and the color filter patterns 170, and the first passivation layer 150, the color filter patterns 170, and the second passivation layer 180 have a plurality of contact windows W. Moreover, the contact windows W expose a portion of the drains 140D. Herein, the second passivation layer 180 is not formed at the sides of each of the contact windows W. The pixel electrodes 190 are conformally disposed on the second passivation layer 180, wherein each of the pixel electrodes 190 is electrically connected to the drain 140D of each of the active devices 140 through one of the contact windows W, respectively. When each of the pixel electrodes 190 is located at the contact windows W, the lower surface of each of the pixel electrodes 190 is only in contact with the sides and a portion of the upper surface of the color filter patterns 170, the sides of the first passivation layer 150, a portion of the upper surface of each drain 140D, and the sides of the second passivation layer 180.
Since a contact angle A between the color filter patterns 170 and the black matrix layer 160 is an obtuse angle (i.e. greater than 90° but less than 180°), a recess C is produced between the upper surface of color filter patterns 170 and the sides of the black matrix layer 160. Consequently, the pixel electrodes 190 formed in subsequent processes have a recess appearing on the surfaces also. Therefore, when a bias is applied to each of the pixel electrodes 190, due to the recess C, the liquid crystal molecules LC located around the recess C have an issue of liquid crystal disclination. Thereby, the display quality of the LCD panel deteriorates. Moreover, if defects (e.g., the scan lines 120 are broken, the scan lines 120 are electrically shorted with the other conductive lines, the data lines 130 are broken, or the data lines 130 are electrically shorted with the other conductive lines) exist in the scan lines 120, the data lines 130, and the active devices after the black matrix layer 160 is formed, the defects are difficult to inspect by optical manners.